Type of epithelium lining the esophagus:

Correct Answer: B

Rationale: The esophagus is lined with stratified squamous non-keratinized epithelium (B), protecting against abrasion from food while retaining flexibility. Simple squamous (A), a single thin layer, suits diffusion (e.g., alveoli), not mechanical stress. Stratified squamous keratinized (C) is in skin, with a tough, dry layer unsuitable for the moist esophagus. Simple columnar (D) lines the stomach and intestines for absorption, not esophageal function. B fits its multilayered, non-keratinized nature resists wear from swallowing, unlike the others, which serve different physiological roles.

Correct Answer: C

Rationale: In mixed venous blood from the inferior vena cava (IVC) at sea level, PN₂ = 620 mmHg (choice C) is inconsistent. Typical mixed venous values are pO₂ ≈ 40 mmHg (choice A), pCO₂ ≈ 46-48 mmHg (choice B), and O₂ content ≈ 150 ml/L (choice D), all aligning with normal physiology (15 vol% for 75% saturation of 20 g/dL Hb). CO₂ content ≈ 540 ml/L (choice E) fits the higher venous CO₂ (≈ 52 vol%). However, PN₂ should approximate arterial levels (≈ 573 mmHg), as nitrogen is inert and equilibrates with atmospheric pressure (760 - 47 - 40 - 100 for arterial). A PN₂ of 620 mmHg exceeds expected values, suggesting an error, possibly from miscalculation or contamination. Normal venous PN₂ doesn't deviate significantly from 573 mmHg, making C the inconsistent value here.

Correct Answer: B

Rationale: Choice B (alveolar ventilation = 7500 ml) is incorrect. Tidal volume (TV) = 500 ml (choice A) is true for a resting adult. Alveolar ventilation (V̇A) = (TV - dead space) × respiratory rate; with TV = 500 ml, dead space = 150 ml, rate = 12/min, V̇A = (500 - 150) × 12 = 4200 ml/min, not 7500 ml/min (likely total ventilation, 500 × 15). Choice C (pulmonary blood flow = 5000 ml/min) matches cardiac output at rest. ' FRC is the volume post-normal expiration (ERV + RV, ≈ 2300 ml). Choice E (physiologic dead space = 150 ml) aligns with anatomic dead space in health. B's overestimation misrepresents alveolar gas exchange volume, making it the exception.

Correct Answer: B

Rationale: 1 g Hb binds 1.34-1.39 ml O₂ (Hüfner's constant), key to O₂ transport. Choice A is false; only 1-2% of O₂ is dissolved (≈0.3 ml/dL at PaO₂ 100 mmHg), 98% is Hb-bound (≈20 ml/dL). Choice C is wrong; anemia lowers O₂ content, not PaO₂ (dissolved O₂), which remains ≈100 mmHg unless lungs fail. Choice D is false; CO₂ is ≈20 times more soluble than O₂, not 200. Choice E is true; CO₂'s curve is steeper due to solubility, not as steep as O₂'s sigmoid shape (misstated). B reflects Hb's O₂-carrying capacity (e.g., 15 g/dL × 1.34 = 20.1 ml/dL), central to transport physiology, making it the accurate statement.

Correct Answer: C

Rationale: surfactant's phospholipid film forms via tubular myelin, a precursor from Type II pneumocytes. Choice A is false; phospholipids (e.g., DPPC) treat IRDS but need proteins (SP-B, SP-C) for full efficacy. Choice B is wrong; smoking reduces surfactant via oxidative damage. Choice D is true; IRDS results from surfactant deficiency, increasing tension and collapsing alveoli. Choice E is false; carbohydrates aid stability, but phospholipids dominate. Tubular myelin, rich in dipalmitoylphosphatidylcholine, reduces surface tension (Laplace's law: P = 2T/r), stabilizing alveoli. C accurately describes this process, critical for lung function.